The invention relates to lamellar clutch discs consisting of sheet steel and arranged in an enclosed housing filled with a viscous liquid medium for a fluid friction clutch.
Fluid friction clutches equipped with lamellar discs are known for example from German Patent No. 2,135,791. These fluid friction clutches are distinguished primarily by the fact that they can transmit a torque upon occurrence of a relative rotational speed between the drive and the driven side of the clutch. The cause of this automatically adjusting torque transmission is to be found in the liquid medium, which owing to its viscosity builds up shearing stresses that oppose the relative rotation of the clutch discs as they are connected to the drive and the driven side alternately. The magnitude of these shearing stresses and hence the amount of the transmissible torque depends, among other things, on the viscosity level of the liquid medium, the temperature, the pressure, the lamella spacing, and the fill of the housing. Advantageously, such fluid friction clutches may be arranged as differentials in the power transmission of a motor vehicle, for example between two wheels of an axle or, in particular, between two axles of a vehicle that are capable of being driven by a common motor.
The use of such fluid friction clutches, however, according to the prevailing operating conditions, calls for a very precise adjustment of the gradient of the torque transmitted by the clutch and a corresponding adaptation of the speeds of the drive and driven sides as functions of time. Thus it has been found that even minor differences in fill of the clutch housing lead to a change in torque performance, and that the characteristic of the clutch in particular is markedly affected by wear.